| The basicranial circulation of Ptomacanthus resembles that in arthrodire placoderms. |
| Some of the most important structural features that mark it as such are in the basicranial region. |
| The posterior part of the craniofacial axis, which has relations only with the cranium, is called the basicranial axis. |
| Of these, one of the largest is the parasphenoid which, in Ichthyopsids, is found underlying the basicranial axis. |
| In the Cervidae and Giraffidae the face is not bent down on the basicranial axis as it is in the Bovidae. |
| In front of the presphenoid the basicranial axis is continued by the mesethmoid. |
